Scalable Low-Band-Gap Sb₂Se₃ Thin-Film Photocathodes for Efficient Visible-Near-Infrared Solar Hydrogen Evolution

A highly efficient low-band-gap (1.2-0.8 eV) photoelectrode is critical for accomplishing efficient conversion of visible-near-infrared sunlight into storable hydrogen. Herein, we report an Sb₂Se₃ polycrystalline thin-film photocathode having a low band gap (1.2-1.1 eV) for efficient hydrogen evolution for wide solar-spectrum utilization. The photocathode was fabricated by a facile thermal evaporation of a single Sb₂Se₃ powder source onto the Mo-coated soda-lime glass substrate, followed by annealing under Se vapor and surface modification with an antiphotocorrosive CdS/TiO₂ bilayer and Pt catalyst. The fabricated Sb₂Se₃(Se-annealed)/CdS/TiO₂/Pt photocathode achieves a photocurrent density of ca. -8.6 mA cm^-2 at 0 V_RHE, an onset potential of ca. 0.43 V_RHE, a stable photocurrent for over 10 h, and a significant photoresponse up to the near-infrared region (ca. 1040 nm) in near-neutral pH buffered solution (pH 6.5) under AM 1.5G simulated sunlight. The obtained photoelectrochemical performance is attributed to the reliable synthesis of a micrometer-sized Sb₂Se₃ (Se-annealed) thin film as photoabsorber and the successful construction of an appropriate p-n heterojunction at the electrode-liquid interface for effective charge separation. The demonstration of a low-band-gap and high-performance Sb₂Se₃ photocathode with facile fabrication might facilitate the development of cost-effective PEC devices for wide solar-spectrum utilization.